time-to-botec

Benchmark sampling in different programming languages
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mean.js (1396B)

      1 /**
      2 * @license Apache-2.0
      3 *
      4 * Copyright (c) 2018 The Stdlib Authors.
      5 *
      6 * Licensed under the Apache License, Version 2.0 (the "License");
      7 * you may not use this file except in compliance with the License.
      8 * You may obtain a copy of the License at
      9 *
     10 *    http://www.apache.org/licenses/LICENSE-2.0
     11 *
     12 * Unless required by applicable law or agreed to in writing, software
     13 * distributed under the License is distributed on an "AS IS" BASIS,
     14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     15 * See the License for the specific language governing permissions and
     16 * limitations under the License.
     17 */
     18 
     19 'use strict';
     20 
     21 // MODULES //
     22 
     23 var isnan = require( '@stdlib/math/base/assert/is-nan' );
     24 var gamma = require( '@stdlib/math/base/special/gamma' );
     25 var SQRT_TWO = require( '@stdlib/constants/float64/sqrt-two' );
     26 
     27 
     28 // MAIN //
     29 
     30 /**
     31 * Returns the expected value of a chi distribution.
     32 *
     33 * @param {NonNegativeNumber} k - degrees of freedom
     34 * @returns {NonNegativeNumber} expected value
     35 *
     36 * @example
     37 * var v = mean( 9.0 );
     38 * // returns ~2.918
     39 *
     40 * @example
     41 * var v = mean( 1.0 );
     42 * // returns ~0.798
     43 *
     44 * @example
     45 * var v = mean( -0.2 );
     46 * // returns NaN
     47 *
     48 * @example
     49 * var v = mean( NaN );
     50 * // returns NaN
     51 */
     52 function mean( k ) {
     53 	if ( isnan( k ) || k < 0.0 ) {
     54 		return NaN;
     55 	}
     56 	return SQRT_TWO * gamma( ( k+1.0 ) / 2.0 ) / gamma( k / 2.0 );
     57 }
     58 
     59 
     60 // EXPORTS //
     61 
     62 module.exports = mean;